test: fix failing tests

Broken since 69d8ea4a because our fake screen
didn't have a root window and writing the XKB rules prop would happily
segfault. Fix this by setting up the required bits.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Tested-by: Michel Dänzer michel.daenzer@amd.com
1 job for wip/xtest-fixes in 1 minute and 24 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #63051
job

00:01:24